1. Field of the Invention
The present invention relates to a camera with an automatic focusing device, and more particularly to a camera capable of selecting one of two different focal lengths according to the positional change of a main lens system in the axial direction thereof.
2. Description of the Prior Art
A so-called two focal-length camera, capable of switching the focal length of a photographing lens at least between two different values by inserting a subsidiary optical system in the optical axis of a main optical system which can alone take pictures, is already disclosed for example in the Japanese Patent Laid-open Application No. 202431/1983. Said known camera is equipped with an automatic focusing device linked with the main optical system.
However, said known two focal-length camera is provided, in addition to a moving mechanism for focusing the main optical system, with a separate mechanism for moving the main optical system in order to switch the focal length thereof by inserting a subsidiary optical system. For this reason the moving mechanism for the main optical system has to be complicated.
Also in the above-described two focal-length camera, the focusing operation is achieved by the movement of the main optical system only, even after the insertion of the subsidiary optical system. Consequently, in a camera so designed as to achieve automatic focusing by the combined movement of the main optical system and the subsidiary optical system, automatic focusing can only be achieved in the absence of the subsidiary optical system.
Also in the above-described two focal-length camera with known automatic focusing device, information on the lens position transmitted from the main optical system does not contain information on the change of focal length. Thus, in order to compensate the change in aperture resulting from the change in focal length, there should be added a link mechanism for changing the aperture in relation to the movement of the main or subsidiary optical system for changing the focal length. Furthermore, in case of equipping the above-described known two focal-length camera with a flashmatic device, there should be separately added a device for transmitting the information on focal length, so that the mechanism for moving the lens has inevitably to be complicated.